Method of and apparatus for damping tensile stress variations of webs



July 14, 1970 D. HANK 3,52

METHOD OF AND APPARATUS FOR DAMPING TENSILE STRESS VARIATIONS OF WEBS Filed Feb. 28, 1968 INVENTOR DIETRICH HANK BY ATTORNEY.

United States Patent 3,520,485 METHOD OF AND APPARATUS FOR DAMPING TENSILE STRESS VARIATIONS OF WEBS Dietrich Hank, Leipzig, Germany, assignor to VEB Druckmaschinenwerke Leipzig, Leipzig, Germany,

a corporation of Germany Filed Feb. 28, 1968, Ser. No. 709,108 Int. Cl. B65h 77/00 U.S. Cl. 242-7543 3 Claims ABSTRACT OF THE DISCLOSURE A tensile stress variation damping and tension controlling unwinding device for use with printing machines or rewinders, wherein a web is fed from a braked roll to two pairs of spaced feeding rollers, with a dancing roller disposed freely movable on the web in a noose between the two pairs of feeding rollers. The two pairs of feeding rollers feed the web in equal lengths with equal circumferential speeds to and from the noose containing the dancing roller and a means for braking the brake roller controlled by movements of the dancing roller is provided such that the Web elongation is controlled so as to have the same mean tension and, therefore, the same mean expansion between the braked roll and the first pair of feeding rollers, as that of the web between the first pair of feeding rollers and the second pair of feeding rollers.

The present invention relates to a method of and apparatus for damping of tensile stress variations on corebraked rolling devices for webs of paper, plastic film and the like, which can be wound again with constant tensile stress or can be fed to a working machine, for instance, the printing machine, as well as to a device for performing this method.

In rolling devices in which the web to be unwound should stand under a constant tensile stress, the roll to be unwound must be braked at the periphery or at the core. The paper web tension is determined in known devices mostly by its load by means of a so-called dancing roller, which is a roller being low on mass and mostly vertically movable in a paper web noose.

By means of this dancing roller, a speed difference between the speed of the web unwinding from the roll and the speed of the web portion which is rewound and fed to the working machine, respectively, is obtained, which speed difference is exploited for the production of control signals for the braking of the roller. If for instance the rewinding speed rises or the braking of the roll is too great, then the dancing roller is lifted and by this movement a signal for the reduction of the braking eifect is emitted. If, however, the rewinding speed or the brake force on the roll is lowered, then the dancing roller is lowered and increases indirectly the braking of the roll. In order to obtain the described movements of the dancing roller it must be disposed between the braked roll and the feeding devices removing he web, for instance, the driven feeding rollers for the paper web.

The dancing roller reacts to slowly occurring speed differences between the roll and the feeding rollers and the paper web tension is determined by the force with which the dancing rolller presses into the noose of the web, depending upon the weight of the dancing roller and upon bearings and the like lifted with the dancing roller, respectively. In order to render possible adjustment of small est values of the web tension, and to make possible a sensitive control of the paper web tension, the dancing roller is mounted, liftably and lowerably with low friction, as well as rotatably, and is more or less strongly balanced 3 ,520,485 Patented July 14, 1970 out by counter-weights. This requires again a strong damping of the vertical movement of the dancing roller, in order to obtain a stabile control reaction. This strong damping of the vertical movement of the dancing roller, as well as its mass inertia have the disadvantage, that short duration and periodically occurring speed variations, as they occur for instance, in case of non-round running rollers, cannot be controlled instead leading to high web tension points, which are fed further up to points beyond the feeding rollers and which, due to the inertia of the dancing roller and its damping, cannot be equalized. The occurring web tension points can lead to a tearing of the web or to a remaining deformation of the latter; smaller web tension variations lead to difficulties during the further working of the paper web.

In similar manner, other devices are effective, which infiuence the web in the sense of a production and maintenance of a predetermined web tension, for instance, drives by means of torque couplings and the like.

It is one object of the present invention, to provide a method of damping tensile stress variations on corebraked rolling devices for webs of paper, plastic film and the like, wherein the drawbacks of the known methods and of the devices operating in accordance with these methods are removed.

It is another object of the present invention to provide a method of damping tensile stress variations on corebraked rolling devices for webs of paper, plastic film and the like, wherein the influence of the web tension variations or speed variations upon the dancing roller are designed such, that the damping of the dancing roller can be omitted and at the same time it is assured, that the effect of high points of the web tension and speed variations upon the dancing roller cannot lead to an increase of the web tension, and wherein, the dancing roller is movable according to variations in the elongation of the web on which it is disposed and is designed with the least possible mass, so that it can be adjusted extremely easily and by the smallest forces and, on the other hand, wherein its movement is not dampened and no resonance appearances and non-stabilities can occur in the control, and where the control of the Web tension in an indirect manner is quite exact. The requirements contradict each other partly, and it appears according to the present status of the prior art, not possible to solve easily this complex task. In accordance with the present invention this task is solved by a method, in which the indirect measuring of the web speed by means of a dancing roller takes place, by means of the measuring web length variation caused by the average web tension from the roller up to a moment equalization device and comparison of the web length variation with the web length variation between the dancing roller and the moment equalization device.

It is still another object of the present invention to provide an apparatus for damping tensile stress variations of webs, comprising a dancing roller disposed between two feeding rollers or pairs of feeding rollers driven synchronously relative to each other, whereby the feeding roller or a corresponding pair of feeding rollers pointing to the unwinding is in the position to assurne additional movements between the feeding roller or pairs of feeding rollers and the moments occurring during the unwinding in and against the direction of movement of the web, respectively.

A spring-biased roller can be dispensed with, if the web section between the roller and the first feeding roller is long enough, so that a sufficient balancing of the web speed variations is assured.

With these and other objects in view, which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawing, in which the only figure is a schematic showing of the arrangement of the feeding roller relative to the dancing roller.

Referring now to the drawing, a paper web 2 is guided from a braked roll 1 over a spring-biased roller 3 and a feeding roller 4, against which a pressure roller 5 exerts pressure, as well as a guiding roller 6, below a dancing roller 7 over a further feeding roller 8 and a further pressure roller 9 to a working machine. The dancing roller 7 is secured to a two-armed lever 10, which is immovably mounted in a lever bearing 11 for a swinging movement and at its free end is connected with brake rods 12, such that a downward movement of the dancing roller 7 causes an increase of the braking effect. It is to be understood, that the braking can be performed by the dancing roller by any known manner. In the first paper web section 13, which extends from the braked roll 1 to the feeding roller 4 and the pressure roller 5, the paper web 2 is expanded for an amount, which is dependent upon the web tension, the variations of which are balanced out to a certain degree by the spring-biased roller 3. The web tension is determined by the braking moment on the braked roll 1 and by the moment value of its diameter. At constant paper web tension, the peripheral speed of the braked roll 1 corresponds with the feed speed of the web 2 between the feeding roller 4 and the pressure roller 5. Speed differences between the peripheral speed of the braked roll 1 and the feed speed of the paper web 2 between the feeding roller 4 and the pressure roller 5 are effective in the first paper web section 13 merely as web tension variations and, thereby, also as variations of the expansion of the paper web.

In the second paper web section 14, which extends from the feeding roller 4 with its pressure roller 5 up to the feed roller 8 with its pressure roller 9, no speed differences of the paper web can occur, since the feeding rollers 4 and 8 feed the paper web 2 with constant speed. The feeding rollers 4 and 8 are operatively interconnected by a common drive means 15 composing an endless chain or belt, or the like whereupon both feeding rollers 4 and 8 feed the web 2 with the exact same speed. The web tension in the second paper web section 14 and, thereby, also the extension of the paper web is determined by the load of the web by means of the dancing roller 7.

By the dancing roller 7, the braking of the braked roll 1 is controlled in such manner that, in the first and in the second web sections equal expansions occur. In case of equal expansion of the web in both web sections, thus equal web tensions throughout, the dancer roller 7 is disposed at a level position, in which it exerts just such braking force on the braked roll 1 by means of the lever and the brake rod 12, which assures the correct webtension and extension in the first web section 13. If, in connection with this braking, the web tension is lowered in the first web section 13, then the extension or expansion of the paper web is lowered also in the first web section 13. The paper web fed by means of the feed roller 4 in the second web section 14 is expanded to a length, which corresponds with the load of the web by means of the dancing roller 7 and due to this expansion, the dancing roller 7 lowers slightly. The lowering of the dancing roller 7 causes an increased braking of the braked roll 1, so that the web tension and, thereby, also the expansion of the paper web 2 increases in the first web section 13. If the expansion of the web 2 in the first web section 13 is greater than in the second web section 14, then the paper web fed over the feeding roller 4 contracts due to the lesser load in the second web section 14 and thereby lifts the dancing roller 7 for a mini mum amount, so that the braking of the braked roll 1 is reduced.

The method of control of the paper web tension by the expedient of the control of the expansion of the paper web brings about a stabile control response of the control cycle under all prevailing working conditions and makes superfluous any damping of the dancing roller movement. High points of the web tension cannot become effective with appreciable intensity over the second web section and the fine-responsive control which is fast, due to the lack of damping maintains the value of an occurring high point of the web tension within tolerable limits.

While I have disclosed one embodiment of the present invention, it is to be understood that this embodiment is given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

I claim:

1. A method of damping the tensile stress variations and of controlling of the web tension on core-braked rolling devices for webs of flexible material as paper, plastic film and the like by means of a dancing roller, comprising the steps of feeding a web wound on a braked roll to, and by, a first feeding roller means, said web therebetween constituting a first web section having a first web section tension therealong caused by a braking force acting on said braked roll,

feeding said web by and from said first feeding roller means, and by, a second feeding roller means having the exact same circumferential speed as that of said first feeding roller means, said first and second feeding roller means being operatively interconnected by a common drive means, said first feeding roller means and said second feeding roller means feeding said web in equal lengths, said web therebetween constituting a second web section,

loading said second web section by a dancing roller, said loading by said dancing roller causing a second web section tension, said dancing roller comparing the elongation of said first web section caused by the average first web section tension with the elongation of said second web section caused by the loading of said second web section by said dancing roller, a difference between said first web section elongation and said second web section elongation causing a lowering or raising of said dancing roller, a lowering of said dancing roller causing an increase of the braking force of said braked roll and a raising of said dancing roller causing a decrease of the braking force of said braked roll in such a mannet, that said first web section elongation and also said first web section tension, caused by said braking force becomes equal to said second web section elongation and also said second web section tension.

2. An apparatus for damping of tensile stress variations and for controlling of the web tension on corebraked unwinding devices for webs of flexible material, such as paper, plastic film and the like, comprising:

a braked roll having a web wound thereon,

a first feeding roller means spaced from said braked roll for feeding the web from said braked roll to said first feeding roller means, said web therebetween constituting a first web section,

means for braking said braked roll, said first web section having a first web section tension caused by the braking force acting on said brake roll as a result of said braking means,

a second feeding roller means for feeding said web by and from said first feeding roller means, and said first roller means and said second roller means feeding said web in equal lengths,

means operatively interconnecting said first and second feeding roller means such that said second feeding roller means has the exact same circumferential speed as that of said first feeding roller means,

said web between said first and second feeding roller means constituting a second web section,

a dancing roller movably disposed loadingly on said second web section, causing a second web section 5 6 tension, on said second web section, said dancing section elongation and also said second web section roller comparing the elongation of said first web sectension. tion caused by the average first web section tension 3. The apparatus, as set forth in claim 2, wherein: with the elongation of said second Web section said means operatively interconnecting said first and caused by the loading of said second web section second feeding roller means comprises an endless by said dancing roller in that a dilference between 5 belt, operatively linking said first and second feeding said first web section elongation and said second ro'ller means. web section elongation causing a lowering or raising of said dancing roller, References Cited said dancing rolileighoperaltively congecteiddto said brlalk- 10 UNITED STATES PATENTS mg means sue a a oweringo sa1 ancing ro er causes an increase of the braking force of said braked ggxg roll and a ralsing of said danclng roller causing a 3,083,602 4/1963 Obershain 242*7543 decrease of the braking force of said braked roll in such a manner, that said first web section elonga- 15 NATHAN LOUIS MINTZ Primary Examiner tion and also said first web section tension, caused by said braking force becomes equal to said second web 

